Temperature measuring apparatus



Jan. 11, 1944. E. M. SMITH TEMPERATURE MEASURING APPARATUS Filed Aug. 2. 1940 I I llllul INVENTOR. V

EDGAR M. SMITH ORNEY Patented Jan. 11, 1944 TEMPERATURE MEASURING APPARATUS i Edgar M. Smith, Trenton, N. J., asslgnor to The Brown Instrument Company, Philadelphia, Pa .a corporation of Pennsylvania Application August 2,1940 Serial No. 349,769

H 8 Claims. The present invention relates to electrical measand particularly to measuring instruments of the Wheatstone bridge type, the state of balance'or unbalance of which is indicated bya sensitive indicating instrument having a deflectable element, utilized for measuring the magnitudes of a pinrality or unknown resistances.

My present invention has especial utility in temperature indicating systems. and particularly uring' instruments of the Wheatstone bridge type.

Fig. 3 is a sectional view on the line AA of the switch mechanism shown in Fig. 2. a

In Fig. l I have illustrated, more or less diagrammatically, the use of my invention in a temperature measuring system in which a plurality of identical temperature responsive resistances I located at-diiferent remote points where it is desired to determine the temperature, are

in such systems which utilize a single instrument to indicate the temperature at any of a number of remote points by means of a plurality 01' search resistances located at various remote points where it is desired to ascertain the temperature.

An object of the invention is to provide an in detail hereinafter.

improved measuring instrument-ofthe type referred to above in which the connections for effecting a measurement of the unknown .resistances are accomplished bya single switching device whereby the manual operations required for eifecting the measurements are reduced to a minimum.

Another object of the invention is to provide an improved switching device foruse in measuring instruments of the type referred to above adapted to be successively connected or switched inton one arm of a Wheatstone bridge network 2 by a novel switch. mechanism 3 to be described Switch mechanism 3 is manually operable to switch the resistances I into the bridge network in succession by manipulation 01' a knob. 4. v Energizing electromotive force is supplied the bridge network 2 under control of the switch mechanism I'by a battery 5 which is connected across the energizing terminals 6 and l of the bridge network. An adjustable resistance 8 is preferably provided in the battery connection to facilitate the adjustment ofthe electromotive force applied to the bridge network to the desired value.

in which slamming of the indicating instrument deflecting element or pointer during the time the switching operation is being eflected is prevented.

A further object of the invention is to provide an improved switching device for use in measuring instruments of the type referred to above whichldisconnects the battery or energizing source of electromotive force from the bridge when in its off position and only in that position.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects obtained with its use, reference should be had to the accompanying drawing and descriptive matter in which I have illustrated end described a preferred embodiment of the invention;

Of the drawing: v Fig. 1 is a diagrammatic representation of a Wheatstone bridge resistance thermometer type measuring instrument provided with switching mechanism in accordance with my invention;

Fig. 2 is a detail view, parts in elevation, of a preferred form of the switching mechanism of my invention with'the cover removed; and.

- ance of the bridge network 2 is ascertained by The other arms of the bridge network 2 include fixed resistances 9, I0 and II which are suitably proportioned to the resistances of the resistances i when the latter are subjected to a predetermined temperature. 7

The state of balance and the extent of unbalmeans of an electrical indicating instrument I! which may be a sensitive volt-meter or galvanometer andwhich is connected across the balancing terminals 13 and M of the bridge network. The indicating instrument i2 is provided with the usual deflecting pointer l5 and dial it,- the latter having appropriate scale divisions and temperature markings for the range of temperatures to be measured. The instrument I 2 may desirably be provided with the usual zero adiustment screw, not shown in order not to confuse the drawing, which changes the position of the pointer 15 with respect to the dial I 6 by moving the fixed abutment of the spring which urges the pointer Hi to its zero position.

The knob 4 of switch mechanism 3 is connected rigidly to a shaft I! which, in turn, is

mechanically connected to and is adapted, when rotatedby manipulation of knob 4, to actuate a plurality of difierent rotary switches. These rotary switches control the supply of energizing electromotive force to the bridge network 2 from the battery 5, are adapted to successively connect the temperature responsive resistances i into ed on a circular disc 2| slightly more than even number of index points.

the bridge network 2 and are also adapted to sistance 8 to the bridge energizing junction 1 I and the positive terminal of the battery is connected by a conductor l3 to the section IQ of a split ring having a second section 20. The ring sections I3 and 20, as seen in Figs; 2 and 3, are insulated from each other and are rigidly mountoi' Bakelite or other suitable insulating material, being riveted or otherwise secured thereto. The ring sections I9 and are so positioned on disc 2| coincident with the center or shaft I'I which extends through the disc 2|. supported for rotation by a bearing 22 provided in the disc 2|.

The ring section 20 is connected by a con ductor 23 to the bridge energizing junction 8 and is adapted to be electrically connected to the ring section I! and thereby to the positive terminal of battery and 23. The brushes-24, and 26 are spaced 90 apart on a circle the same diameter as-the ring comprised oi sections l9 and 20 and are rigidly secured by'screw orother suitable'means to a circular disc 21 of insulating material. The disc 2! center thereof on shaft l1.

When the brushes 24, 25 and 26 are in the posithat their center is is rigidly mounted at the.

The shaft I1 is 5 by means or three flexible electrically connected brushes indicated at 24, 25

the brushes 24, 25 and 23 that when the latter are adjusted to the "of!" position of the switch mechanism, one end of brush 23 is in engagement with the ring section 20, which section i then not energized. At its other end, the brush 28 is adapted, when moved, to successively engage each one of a number of spaced arcuate contact segments 3|) which are rigidly secured to the insulating block 2|. end of the brush 23- is desirably of sufllcient width to bridge'the gap between the contact segments 30. The contact segments are evenly spaced in a circle on the block positioned relatively to circle, and are each electrically connected with one end of a respective temperature responsive resistance I. To this end the contact segments 33 are desirably provided with soldering lugs the block 2| as seen in nected by a conductor 33 to the balancing terminal l4 of the bridge network 2. The contact segments 32 are evenly spaced in a'circle on the block 2|- with the opening for shaft |1 being at tion wherein they engage only the ring section It,

the supply of energizing electromotive force from the battery 5 to the bridge network 2 is prevented. The switch mechanism is then in its "01? position. when the brushes 24, 25 and 26 are moved downward, as seen in Fig. l'or clockwise as seen in Fig. 2, however, they electrically connectthe ring sections l9 and 20 and thereby complete the energizing circuit to bridge network 2 from battery 5.- This energizing circuit may be traced from the positive terminal of battery 5 to conductor l8, ring section l9, brushes 24, 25 and 26, ring section 20, conductor 23 to the bridge energizing junction 5, the bridge network 2, the bridge energizing junction 1 negative terminal of battery 5.

In order that there will be only one position of the brushes 24, 25 and 26 in which the supply of energizing electromotive force to the bridge network is cut of! or in other words in which the switch mechanism 3 is in its "oil position, the ring section I9 is. made slightly longer than the section 20. When this is done, it will be seen by reference to Fig. tion of the brushes 24, 25 and 23 except that shown the brushes will interconnect the ring sections 19 and 20. Preferably the ringsection I9 is made one index point longer than the section 20 for switch mechanisms having an odd number of index points and two index points longer than the section 20 for switch mechanisms having an 21 as shown. The brush 28 is adapted-to engage 20 at one end thereof the ring sections I9 and 2 that in every other posi-.

which are rigidly and resistance 8 back to the and is preferably of sufiicient width to bridge the gap between those sections. The brush 28 is so the bridge junctions the center of said circle, and are each connected to the other terminals of a respective temperature responsive resistance I.

The brushes 28 and 29 and the associatedcon tact segments 30 and 32 are so arranged that on rotation of the shaft II, the temperature responsive resistances l are successively connected into the bridge network 2 between the junctions 6 and I4.

When the brushes 28 and 23 are adjusted from one contact segment 30 and 32, respectively, to the next, two corresponding and adjacent temperature responsive resistances I are simultaneously connected into the bridge network'2 since the brushes 28 and 23 are wide enough to bridge the gap between adjacent contact segments 33 and 32 whereupon the eflective resistance between 5 and I4 is substantially reduced. This reduction in resistance between bridge junctions is sudden and produces an appreciable unbalance of the bridge network and' thereby tends to cause a violent slamming of the indicating instrument pointer l5.

In accordance with my present invention, this undesirable action is avoided by shunting the terminals of "a pair of flexible brushes 35 and 35 are provided.

The contact segments 34 are mounted on the insulating block 2| and are disposed in a. circle about the opening for shaft IT. The brushes 35 and 33 are mounted closely adjacent each other on the insulating block 21 and are electrically connected to each other. The brushes 35 and 36 are of such width relative to the width of the contact segments 34 that when a single temperature responsive resistance is connected into the bridge network 2, both of the brushes 35 and 36 are in engagement with one only of the contacts 34. Preferably the brushes 35 and This , 2|, the opening in the block for shaft being at the center of said the instrument |2 whenever the switch mechanism is adjusted to switch a dii-- assane 36 are of greater width than the width of a contact segment 34, but are slightly less than the total width of a contact segment 35 plus the width of the gaps on both sides,'as shown in Fig. 2-. Thus, on only slight movement of the brushes 35 means. A scale 38 having suitable markings or index points identifying each of the temperature responsive resistances I and also the oil" position of the switch mechanism is provided on and 38 and before. the brushes 28 and 29 have been adjusted from one contact segment 30 and feet of the brushes 35 and 36 thus bridging two adjacent contacts 34 is to shunt the instrument terminals and thereby prevent slamming of the instrument pointer I5 as the switch mechanism 3 i adjusted to connect a different one of the temperature responsive resistances bridge network 2.

It is noted that with this provision for preventing slamming of the instrument pointer l5, it is not necessary to interrupt the supply of,

energizing electromotive force to the bridge net-- work 2 whenever a different one of the resistances I is connected in the bridge network, nor is it necessary to provide narrow contact segments and brushes to prevent the simultaneorder to reduce theicost of construction of said mechanism. It is noted that when the contact segments 30, 32 and 34 are arranged in rings of different diameter, the arcuate length of the contact segments 30, 32 and '34 must be different if the same spacing'between the contacts is to be maintained. Therefore, in order to provide rings of contact segments of uniform length in quantity production it would require the use of three different tools for stamping out each of the sets of contact segments 30, 32 and 34. In the novel switch mechanism of my invention the number of tools for stamping out the contact segments has been reduced to two by making the smaller contact segment 30 the same I into the the front of the cover 31. I A pointer 39 mounted rigidly on the shaft I1 is disposed in cooperative relation with the scale 38 for indicating the position to which the switch is adjusted. v

With this arrangement the switchmechanism 3 may be readily adjusted by manipulation of the single knob 4 to connect the desired one of thetemperature responsive resistances into the bridge network 2, to shunt the terminals of instrument l2 during the switching operation to prevent slamming thereof, and to deenergize the system when the desired readings have been obtained.

In order not to confuse the drawing only eight contact segments 30, 32 and 34 have been shown in Fig. 1 whereas twenty-sixsuch segments have been shown in Fig. 2. It will be apparent. to

those skilled in the art that the switch mechastrument, a second switching means having a plurality of positions operable coincidentally 'with the first mentioned switching means for size as the contact-segments 32 which are on a smaller diameter ring and by making the larger contact segment 30 the same size as the contact .which the switch mechanism is subjected. The .cover 31 'is fitted over the outer or circumferential edge of the disc 2| andis supported thereby, being held rigid therewith by screw or other nism may be provided with any desired number of contact segments to thereby permit the reading of the temperature condition at a corresponding number of remote points.

' While in accordance with the provisions of the statutes, I have illustrated and described the best form of my invention now known to be, it will be apparentto those skilled in the art that changes may be made in the form of the apparatusdisclosed without departing from the spirit of my invention as set forth in the appended claims, and that in some cases certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

Having now described my invention, what I claimas new and desire to secure by Letters Patent is:

1.. In a measuring system, the combination with a plurality of impedances to be measured of an impedance measuring instrument having, a plurality of energizing terminals, a source of' pedances to said instrument to simultaneously connect more than one impedance to said incontrolling the connection of said source of electrical energy to said instrument, said second switching means having only one position in which said source of electrical energy is disconnected from said instrument, and a third switching means having a plurality of positions operable coincidentally with the first mentioned switching means for shunting the terminals of said instrument to prevent-sudden surges of current in. said instrument during the switching operation due to the simultaneous connection of more than one impedance to said instrument.

2. In a measuring system, the combination with a plurality of impedances to be measured of an impedance measuring instrument having a pluralityof energizing terminals, a source of electrical energy adapted to be connected to the terminals of said instrument for energizing the latter, switching means having a plurality .of

positions for controlling the connection of said impedances to said instrument and arranged during the switching operation of successive impedances to said instrument to simultaneously connect more than one impedance to said instrument, a second switching means having a plurality o; positions for controlling the connectionv of said source of electrical energy to said instrument, said second switching means having only one position in which said source of electrical energy is. disconnected from said instrument, a third switching means having a plurality of positions for shunting the terminals of said instrument to prevent sudden surges of current in said instrument during the switching operation due to the simultaneous connection of more than one impedance to said instrument, and a device common to all of said switching means for actuating the latter to their diflerent positions. v i

3. In a temperature measuring system, the combination with a plurality of temperature responsive resistances to be measured of an electrical measuring instrument having a plurality of energizing terminals and calibrated in terms 7 of temperature for indicating the temperature Y which said source of electrical energy is disconnected from said instrument, a third switching means having a pluralityoi positions for shunting the terminals of said instrument to prevent sudden surges of current in said instrument during the switching operationgdue to the simultaneous connection of more than one resistance of said switching means for selectively actuating the latter to connect a desired one of said resistances to said instrument or to disconnect said source of energy from said instrument.

4. In. a. measuring system, the combination with a plurality of impedances to be measured of an impedance measuring network, a measuring instrument having a plurality of terminals and responsive to a characteristic of said impedance measuring network, a connection between the terminals of said measuring instrument and said impedance measuring network, a source of electrical energy adapted to be connected to said impedance measuring network for energizing the latter, switching means having a plurality of positions for controlling the connedtion of said impedances to said impedance measuring network and arranged during the switching operation of successive impedances to said network to simultaneously connect more than one of said impedances to said network, a second switching means having a plurality of positions for controlling the connection of said source of electrical energy to said instrument,

said second switching means having only one position in which said source of electrical energy is disconnected from said instrument, and a third switching means having a plurality of positions operable coincidentally with the first mentioned switching means for shunting the terminals or said instrument to prevent surges of current in said instrument during theswitching operation due to the simultaneous connection of more than one impedance to said network. V

5. In a measuring system, the combination with a plurality of impedances to be measured of an impedance measuring network, a measurnected to'said impedance measuring network switching operation of successive impedances to said network to simultaneously connect more than one of said impedances to said network, a-

second switching means having a plurality of positions for controlling the connection of said sourceof electrical energy to said instrument,

, said second switching means having only one position in which said source of electrical energy is disconnected from said instrument, a third switching means having a plurality of positions] I for shunting the terminals of said instrument to prevent surges of current in said instrument durto said instrument, and means common to all ing the switching. operation due to the simultaneous connection or more than one impedance to said network, and a device common to all 01' said switching means for actuating the latter to their diiierent positions.

6. In a temperature measuring system, the combination with a plurality of temperature responsive resistances to be measured of a' resistance measuring network. an electrical instrument having a plurality of terminals and responsive to a characteristic of said resistance measuring network and calibrated in terms of temperature for indicating the temperaturev of said resistances, a connection between the terminals of said measuring instrument and said resistance measuring network, a source of electrical energy adapted to be connected to said resistance measuring network for energizing the latter,

switching means having a plurality of positions 'for controlling the connection of said resistsaid resistance measuring network, a 'third' switching means having a plurality of positions for shunting the terminals of said instrument to prevent surges or current in said instrument during the switching operation due to the simultanecus connection of more than one impedance source of energy from said resistance measuring network.

id impedance measuring network,

'7. In a measuring system, the combination with a plurality oi impedances to be measured oi an impedance measuring network having a pair of balancing terminals and a pair of energizing terminals, a measuring instrument responsive to a characteristic 01' said network, connections between the balancing terminals of said network and said instrument, a source of electrical energy for energizing said network, and a switch mechanism for controlling the connection 01' said impedances and said energizing source to said network and arranged during the switching of successive impedances to said network to simultaneously connect more than one impedance to said network, said switch mechanism including a supporting base, a plurality of contact segment assemblies in the form of circles having difierent diameters secured to said base, separate connections each including one of said impedances between each of the contact segments on one of said circles and a contact segment individual thereto on another of said circles, a plurality of contact rings concentric with the circles of said contact segment assemblies but of diameters different therefrom and from each other and secured to said base, at least one 01 said contact rings being split into two sections one of which is longer than the other, connections between one energizing terminal of. said network and the longer section of said split contact ring including said source of energy, a connection from the shorter'section' of said split contact ring to the other energizing terminal of said network, a connection between another or said contact rings and one of the balancing terminals of said network, a brush supporting structure disposed in cooperative relation with said base and rotatable relatively thereto, the

the contact rings, means to relatively rotate said base and brush supporting structure, a plurality of brushes secured to said brush supporting structure, one of said brushes disposed to successively connect the contact segments of oneof said contact assemblies to said split contact ring, another or said brushes disposed to successively connect the contact segment oisaid another of that they are all adapted to engage the longer section of said split contact ring only in one position of said brush supporting structure relatively to said base, a connection betweenalternate contact segments on another of said contact segment assemblies and one terminal of said instrument, a connectionbetween the remaining contact segmentson said lastmentionedcontact assembly and theother terminal;ot.j-said ment, and another 01 said brushes disposed to connect the contact segments or said last mentioned contact segment assembly to shunt the terminals or said instrument to prevent sudden surges or current in said instrument due to the connection or more than one impedance to said network during the switching operation.

8. In a measuring system, the combination with a plurality of impedances to be measured of an impedance measuring network having a pair of balancing terminals and a pair of energizing terminals, a measuring instrument responsive to a characteristic of said network, connections between the balancing terminals of said network and said instrument, a source of electrical energy for energizing said network, a connection from one terminal of said source to one energizing terminal of said network, and a switch mechanism for controlling the connection of said impedances and the other terminal of said energizing source to said network in such a manner 'to more than one impedance being simultaneously connected to said network including a supporting base, a first contact segment assembly secured to said base and having contact segments all of the same size uniformly disposed in a circle, a. connection from all but one of the contact segments on said first contact segment assembly to one terminal of an individual one of said plurality of impedances to be measured, a contact ring associated with said first contact segment assembly, a connection between said contact ring and one balancing terminal of said network, a second contact segment assembLv secured to said base and having contact segments all of the same size uniformly disposed in a circle concentric with but of different diameter than the circle of said first mentioned contact segment assembly, a connection between atlernate contacts of said second contact assembly and one balancing ter minal of said network,a connection betweenthe remaining contacts of said'contact segment assembly and the other-balancing terminal of said 1 network, a third contact segment assembly se- 4 5 cured to said base and having contact segments uniformly'disposed in .a circle concentric with but-of: diameter, intermediate the diameters of the-circles'of said first and second mentioned contact segment assembly, alternate contact segments of said third mentioned contact segment assembly-being substantially equal in size to the contact'segments of said first and second mentioned contact segment assemblies whereby the spacing between the contact segments of all of the assemblies is approximately the same, and brush means disposed in cooperative relation with each one of said contact segment assemblies and eachof said contact rings to successively connect the contact segments on said first contact segment assembly to said first contact ring and simultaneously to connect the contact segments of said third contact segment assemmy to said second contact ring, and during the 'switching operation to shunt adjacent contact segments bly.

on said second contact segment assem- EDGAR M. SMITH; 

